1. Field of the Invention
The present invention relates to an electromagnetic lock. Such a lock comprises two parts, one of which is fixed while the other is affixed to the element for which one would like to control the closing, such as a door.
2. Discussion of Background Information
The fixed part of the lock consists of an electromagnet and the other part of a metal armature capable of being displaced to counter a return spring. When the armature is facing the electromagnet and the latter is energized, said armature is attracted and it is not possible to control the door as the force needed for pulling the armature away is much greater than the force that could be provided by an average user.
Currently, electromagnetic locks are arranged such that their active surfaces are parallel to the plane of the opening to be controlled. As a result, the necessary force to be applied in order to allow the sliding of the armature in such plane with respect to the electromagnet is minimized. However, the electromagnetic force used to maintain closure is typically far less than the force able to be applied by a user when pulling in such plane.
It is possible to overcome this drawback by increasing the force of the electromagnet, but such an increase translates into an unacceptable increase of the volume of said electromagnet and its cost.
An adequate solution to avoid oversizing the electromagnet consists of providing, on one of the parts of the lock, a protuberance capable of penetrating into a housing or aperture of the other part and of maintaining itself therein as long as the electromagnet is energized.
Such a lock is described, among others, in the document WO 99/18315 and comprises a mobile armature having two truncated, diagonally opposed, protuberances capable of penetrating into corresponding housings of the electromagnet when the armature is facing the electromagnet. Since the height of the aforementioned protuberances is greater than the distance that normally separates the electromagnet and the armature, the armature must be floatingly mounted on its base, which involves the use of two series of opposing springs that keep the armature balanced. This adds unnecessary expense to such a lock because of the use of two springs. Furthermore, the adjustment of the two springs is difficult.